Teletherapy generally employs an irradiation source disposed at a distance from the body to be treated. X-rays and electron beams have been used in teletherapy to treat various cancers. However, X-rays and electron beams exhibit an energy transfer characteristic approaching an exponential attenuation function and are therefore not optimal for treating deeply embedded growths or target areas. Recently, the use of heavy particles, particularly hadrons, in teletherapy has found increasing acceptance, in part because of the ability of heavy particles to penetrate to a specific depth without appreciably harming intervening tissue. In particular, the energy transfer characteristic of hadrons exhibits an inversed depth profile with a Bragg peak at a location where the hadrons deposit most of their energy, which is approximately at the end of the hadrons' path. As a result of this hadron energy transfer characteristic, increased energy can be directed at or deposited in an embedded growth as compared to X-rays and electron beams. Also, less damage to healthy intervening tissue results when hadron beams are used to treat deep-seated tumors or diseased target tissue.
It should be appreciated that the term “hadrons” can refer to a variety of particles, including protons and other ions that are used in therapy. While this document describes treatment as being accomplished with protons, this is not meant to be limiting in any way and other types of hadrons and ions can be included in such discussion where appropriate.
Typically, in a therapy system, the charged protons or ions are focused into narrow, intensity-modulated, scanned pencil beams of variable penetration depth. In this way, the dose profile can be matched to the target volume. In order to ensure complete irradiation of the target growth, a plurality of beams arriving at the embedded growth from several different directions can be used. The volume in which the plurality of beams intersects, whether the beams are provided sequentially or simultaneously, is often referred to as an isocenter. To improve the biological effectiveness of the treatment, the isocenter is collocated with the target growth to deliver the maximum treatment dose to the target volume and to spare the surrounding tissue.
Present teletherapy systems use a gantry apparatus carrying a beam generating and delivery system. The gantry is a motorized or powered apparatus for moving the massive particle delivery system around a patient who is typically immobilized on a treatment table. Since the beam generating and delivery system is large and extremely heavy, such gantry systems are prohibitively expensive, limiting the number of available proton therapy centers that can provide services to patients. Furthermore, the spatial range of such gantry-driven systems is limited due to mechanical constraints. Movement of the beam generating and delivery system from location to location in order to effect the delivery of the plurality of beams leads to an offset in the isocenter which must be carefully adjusted prior to beam delivery. One example of the above-described treatment systems is illustrated in U.S. Pat. No. 6,769,806 to Moyers.
There is thus a need for an improved teletherapy apparatus that overcomes some or all of the above limitations.